Bouzid Choubane

SUITABILITY OF ASPHALT PAVEMENT ANALYZER FOR PREDICTING PAVEMENT RUTTING

Findings are summarized from an investigation performed to evaluate the suitability of a wheel-tracking device known as the asphalt pavement analyzer (APA) for assessing the rutting potential of asphalt mixes. The evaluation process consisted of correlating the APA’s predicted rutting with known field measurements. The correlation between beam and gyratory samples and the testing variability were also investigated. In addition, the APA test results were compared with those obtained using the Georgia loaded-wheel tester. The findings of this investigation indicated that the APA may be an effective tool to rank asphalt mixtures in terms of their respective rut performance. However, for each mixture type, the APA testing variability was significant between tests and between the three testing locations within each test. Differences in rut measurements of up to 4.7 and 6.3 mm were recorded for beam and gyratory samples, respectively. Therefore, using the APA as a clear pass-or-fail criterion for performance prediction purposes of asphalt mixtures may not be appropriate at this time. It should be noted that these findings are based on data collected on three mixes. Therefore, it is suggested that the APA testing variability (testing and testing locations within the device) be further assessed with a wider range of mixtures. The intent of such an assessment should not only be to correlate the APA results with field data but also to develop potential pass-or-fail limits and procedures.

Effect of Tire Rubber Grinding Method on Asphalt-Rubber Binder Characteristics

The results of a study carried out to evaluate the effect of rubber grinding processes on the properties and characteristics of the resulting asphalt-rubber binder are presented. Several ambient and cryogenic ground tire rubber (GTR) materials were evaluated using measurements of surface areas and bulk densities. The rubber materials were then, respectively, mixed with an AC-30 asphalt; the resulting blends were tested to determine the corresponding viscosity, settlement during storage, and potential for binder draindown. The findings indicate that the asphalt-rubber binders produced with rubber from the different grinding processes have measurable differences in properties and storage characteristics that are critical to the performance of the binder in open-graded mixtures. The wet-ground rubber material had substantially lower bulk densities and larger surface areas than rubber resulting from other grinding methods. GTR materials with greater specific surface areas and more irregularly shaped particles produced asphalt-rubber binders with higher viscosities. Binders with the cryogenic ground rubber had the greatest amount of settlement and the least resistance to draindown.

Effects of Water Saturation Level on Resistance of Compacted Hot-Mix Asphalt Samples to Moisture-Induced Damage

The Florida Department of Transportation (FDOT) initiated monitoring of its first Superpave section on I-75 in Columbia County for stripping potential using AASHTO T 283, which specifies that all conditioned test samples be saturated to between 55 and 80 percent based on 7 ± 1 percent air voids. A fairly large saturation range is allowed because it was thought that mixtures may have different percentages of permeable air voids. However, the potential interaction between air void content and the level of saturation has not been fully investigated. It is also not clear whether test results from samples saturated to 55 percent are comparable with those of the same mixture saturated to 80 percent for a similar air void content. Therefore, although FDOT adopted AASHTO T 283, it also initiated a parallel study on the effects of different degrees of saturation on moisture damage. Findings are reported of both the ongoing monitoring of the I-75 project for potential stripping and the investigation of the effects of different levels of saturation on moisture susceptibility test results as determined using AASHTO T 283.

Rut Initiation Mechanisms in Asphalt Mixtures as Generated Under Accelerated Pavement Testing

The Florida Department of Transportation (FDOT) conducted an experiment to address the effects of polymer modifiers on the performance of Superpave® mixes by using a heavy vehicle simulator. Two fine-graded Superpave mixes were considered. One mix included a virgin binder meeting the requirements of PG 67-22, and the other contained a styrene-butadiene-styrene polymer (SBS)-modified binder meeting those of PG 76-22. Both respective mixes contained the same effective binder content, aggregate components, and gradation. The mixes were designed for 10 million to 30 million equivalent single-axle loads with the use of the standard Superpave mix design methodology. During placement of these mixes, all standard FDOT density requirements and acceptance criteria were applicable. The subsequent investigation showed that the sections with SBS-modified mixture significantly outperformed those with the unmodified mixture. It was also determined that rutting in the unmodified mixture was primarily a function of shear ...

Impact of Wide-Base Single Tires on Pavement Damage

Dual tires have traditionally been used to limit pavement damage by efficiently distributing axle loads over a larger contact area than single tires. However, in recent years, the trucking industry, stating economic and safety benefits, has promoted the use of wide-base single tires. The Super Single tire, an early type of wide-base tire, proved inadequate and induced excessive pavement damage. By contrast, the new generation wide-base tires have contact areas that approach those of dual tires and offer the potential for improved performance. The Florida Department of Transportation investigated the pavement damage potential of four tire types, including a conventional dual tire (11R22.5), a Super Single (425/65R22.5), and two newly designed wide-base single tires (445/50R22.5 and 455/55R22.5 respectively). A controlled accelerated pavement testing program, in addition to theoretical modeling, was performed to determine critical pavement response parameters. Pavement damage was measured in terms of rutting and fatigue cracking (bottom-up or top-down), the predominant distresses in Florida. The investigation revealed that the 455-mm wide-base tire performed as well as the dual tire. By comparison, the 445-mm wide-base tire was shown to create more rut damage on a dense-graded pavement surface and was predicted to create more bottom-up cracking than a dual tire. As expected, the Super Single induced the most damage to the pavement.

Experimental Evaluation of a Pavement Imaging System: Florida Department of Transportation’s Multipurpose Survey Vehicle

The Florida Department of Transportation (FDOT) has acquired and validated a multifunctional survey vehicle for the collection of highway pavement-related data at normal operating speeds. With its ability to collect pavement, right-of-way, and side-view images together with position location, cross-slope, grade, curvature, rutting, and roughness data, this state-of-the-art vehicle enables the rapid and automated evaluation of roadway performance and identification of hazardous conditions. Manual surveys that involve a high degree of subjectivity, a low production rate, and exposure to hazardous conditions are still the most widely used means for evaluating pavement distress. The pavement evaluation subsystem of the FDOT survey vehicle represents an efficient, cost-effective, and safe alternative for the collection and evaluation of pavement distress data. In the research reported in this paper, the precision and accuracy of the pavement imaging subsystem was tested under different lighting conditions, spe...

Nuclear Density Readings and Core Densities: A Comparative Study

Presented are the findings of an investigation performed to identify possible correlations between nuclear density gauge readings and core density results. The nuclear density data were collected on a Superpave section of I-95 in Brevard County, Florida. Core samples also were obtained from this section for laboratory density determination. Five gauge units [Troxler models 3401, 3440 (two units), 3450, and 4640] and three core density methods (Florida test method FM 1-T 166, ASTM D1188, and dimensional analysis) were considered. The relationships among the core density results were analyzed, then an investigation of the correlation among the different gauges used in this study was evaluated. Finally, the performance of each of the units with respect to the core density results was assessed. The findings indicated that the five nuclear gauge density units did not always produce similar results and did not consistently correlate with the core densities. In addition, the nuclear density testing variability differed not only from gauge to gauge but also from location to location within each gauge.

Precision of locked-wheel testers for measurement of roadway surface friction characteristics

The present state-of-the-art locked-wheel testers for roadway surface friction evaluation are fully automated. As with any testing using subjectdriven instrumented devices, the major concerns of the end usefulness of the resulting data are accuracy and precision. Although a level of uncertainty is always inherent in any measurement process, it must also be appropriately quantified or assessed. Therefore, the Florida Department of Transportation (FDOT) initiated a field study to assess the level of precision of its own locked-wheel testers for field measurements. Friction measurements were acquired by using four friction locked-wheel testers concurrently on a number of asphalt section sites. These test sections were randomly selected to include both open- and dense-graded surface mixtures. The collected friction data were first analyzed to determine the friction characteristics at each test location, in terms of a friction number at 40 mph with a standard ribbed test tire (FN40R). The results were then used as a basis for an evaluation of the repeatability and reproducibility of the friction units. In addition, the effects of pavement surface texture on friction measurements were assessed. A description of the testing program, the data collection effort, and the subsequent analyses and findings is presented.

Evaluation of Coarse- and Fine-Graded Superpave Mixtures Under Accelerated Pavement Testing

Initial Superpave® implementation guidelines encouraged mix designers to develop coarse gradations for higher-traffic-level mixtures, as this was thought to produce a more robust aggregate structure. Consequently, many agencies have specified the use of a coarse-graded asphalt mixture on high-volume facilities. However, target density can be difficult to obtain while compacting coarse-graded mixtures, and control of volumetric properties is harder to maintain than it is for fine-graded mixtures. The Florida Department of Transportation (FDOT) conducted an experiment to assess the rutting performance of coarse- and fine-graded Superpave mixtures under accelerated pavement testing (APT). Both mixtures consisted of aggregate from the same source and were made with virgin binder meeting the requirements of performance grade 67-22. Both mixtures contained the same effective binder content and were designed for 10 million to 30 million equivalent single axle loads, according to the standard Superpave mix design...

Measuring Pavement Friction Characteristics at Variable Speeds for Added Safety

Pavement friction testing is frequently conducted in accordance with the provisions outlined in ASTM E 274, “Standard Test Method for Skid Resistance of Paved Surfaces Using a Full-Scale Tire.” The standard speed of testing in Florida is 40 mph (64.4 km/h). However, due to safety concerns related to testing on high-speed facilities, considerable attention has been focused in recent years on height-sensor based (non-contact) technology. It is potentially well suited for surveying the surface texture characteristics of pavement sections while operating at highway speed. Although the height-sensor based technology has been available since the 1960s, it continues to mature. A considerable amount of research has been conducted to gain further understanding on the factors affecting high-speed pavement surface surveying from both the analytical and experimental points of view. Still some problems have not fully been resolved, particularly in the interpretation of the measured data and selection of adequate sensing technology (or sensor designs). The Florida Department of Transportation (FDOT) initiated the present study to assess the feasibility of using high-speed, laser-based sensors to quantify the texture and friction characteristics of asphalt pavements. The main objective of this study is to provide for a safer, faster and more appropriate method of estimating pavement friction characteristics on high-speed facilities, ramps, and at other potentially hazardous sites. Further, it is also intended to provide for a means to obtain a measure of International Friction Index (IFI) in accordance with ASTM E 1960. This paper presents a description of the FDOT testing program, the data collection effort, as well as the subsequent analyses and findings.